For years, dental compositions such as tooth whiteners and fluoride gels have been applied to the teeth of patients in need of a cosmetic or therapeutic dental treatment. These compositions, usually in the form of a gel, paste or foam, have traditionally been comprised of one or more active therapeutic agents dissolved in an aqueous or water-soluble carrier. An aqueous or water-soluble carrier was used because the majority of dental therapeutic agents, such as inorganic fluorides (anticaries agents), peroxides (tooth whitening agents), chlorhexidine (an antibacterial agent), potassium nitrate (a tooth desensitizing agent) and polyphosphates (tartar control agents) are water-soluble compounds. Most of these compositions are intended to be brushed, rinsed or sprayed onto the teeth for a short period of time, for instance the few minutes during which the average individual will brush his or her teeth.
A number of dental treatments, though, require that a therapeutic agent be in contact for a much longer period of time than is practical by the above methods. Arch-shaped dental trays have been developed that are either customized by methods known in the art, or are in the one-size-fits-all category. Such trays are typically loaded with a small amount of a dental composition, and then placed over the teeth of the upper arch, the lower arch, or both arches simultaneously (using two dental trays at the same time). While such devices and methods tend to greatly increase the length of time a dental composition remains in contact with the tooth surfaces, said compositions still remain highly soluble in water. Being soluble in water, these compositions rapidly dissolve and leach out of the dental tray once placed in the mouth in contact with saliva. Upon dilution, these compositions are seen to quickly migrate out of the dental tray and thus become free to contact areas of the oral cavity not intended for treatment. The diluted compositions may also be swallowed by the patient, for instance when a tooth whitening composition is loaded into a dental tray and placed in the oral cavity against the teeth for an extended period of time, such as overnight while the patient is asleep. The whitening composition within the tray gradually becomes lower in viscosity due to dilution with saliva, migrates out of the dental tray, and is unintentionally swallowed by the patient. Repeated ingestion of the oxidizing ingredients of such compositions may be detrimental to the tissue surfaces of the digestive tract.
Other delivery modes for applying tooth whitening compositions to the surfaces of the teeth are available, each with different degrees of acceptance by the consumer and effectiveness. There exists thin plastic strips that are coated on one side with a layer of tooth whitening gel and stored until use against a release backing (similar to that used for a pressure sensitive label), in a unit dose laminated pouch. When a consumer or patient desires tooth whitening, the pouch is opened, the strip/gel device combination is removed from the release backing, and the user carefully places the strip on the teeth to be whitened (gel side against the teeth). While this approach has been shown to be safe and effective, the strips are somewhat cumbersome to handle and position, and there are instances where the entire plastic strip and associated gel have been swallowed by the consumer. Furthermore, the strip of plastic must be removed at some point in time, typically 20-45 minutes following initial placement against the teeth, and following removal of the strip the patient will have to dispose of the strip and often rinse their mouth to remove excess whitening gel. This can be inconvenient if done anywhere other than in the privacy of one's home or office. If the tooth whitening gel is also completely water soluble, salivary intrusion and gel dissolution can occurs in a similar fashion to that observed with dental whitening trays. An additional drawback of these strips is that the hydrogen peroxide active ingredient in the gel tends to degrade faster over time as a thin layer, due to the relationship of hydrogen peroxide stability to surface area/volume ratios. In general, a high surface area to volume ratio leads to more rapid degradation of hydrogen peroxide, said high ratio being inherent in the thin layer of tooth bleaching gel deposited on the backing material of these strips.
Efforts have been made to reduce the perceptibility of dental devices placed in the oral cavity to deliver therapeutic compositions to the tooth and gum surfaces, however to date the trade-offs made in order to improve patient compliance and comfort have resulted in products that do not perform as well as the traditional and more cumbersome methods, such as custom tray-administered tooth whitening. Brush-on products, while being simple to use and easy to apply, may dissolve or erode quickly after being deposited on the tooth surfaces and therefore are not as effective as products that remain in contact with the tooth surfaces for extended periods of time.